226 PRACTICAL ORGANIC CHEMISTRY hot water, then with- warm dilute caustic soda and water again. Yield, 10 12 grams. Sublimation. A portion of the dry substance may be purified by sublimation. It is placed (23 grams) on a large watch-glass, which is heated on the sand-bath over a very small flame. The watch-glass is covered with a sheet of filter paper, which is kept flat by a funnel placed above. After five minutes or so pale yellow, needle-shaped crystals of anthraquinone will have sublimed on to the filter paper. ,CHV /COX C0H ' I \CflH4 + 2Cr03 + 6C,H4Oa = CflH4< >CrtH.,+ XCH/ XCO" Properties. Yellow needles: m. p. 277 ; sublimes at 250 ; b. p. 382" ; insoluble in water, soluble in acetic acid, less soluble in benzene and other organic solvents. Reaction. Add a little dilute caustic soda to a small quantity of anthraquinone, and then a little zinc dust. On heating to boiling, an intense red colouration is produced, which disappear^ on shaking. Sodium oxanthranolate, C<5H., . formed, which oxidises in the air to anthraquinone. Appendix, p. 316. PREPARATION 109. Anthraquinone /^monosulphonate of Sodium, CGH 4/Ł°\C0H3.SOaNa + H,O Graebe, Liebermann, Annalcn, 1871,160, 131 ; A. G. Perkm, Private communication. 30 grms. anthraquinone. 30 fuming sulphuric acid (40 per cent. SO;.).1 The 40 per cent, fuming sulphuric acid is removed from tin; bottle by cautiously melting it in a sand-bath, and it is then weighed, out in a flask (Ł litre). The anthraquinone is added, and the flask attached by a cork to an air-condenser. Tin.? 1 As fuming sulphuric acid is difficult to keep In an ordinary stoppered butt I** without absorbing moisture, it is advisable to coat the stopper with a layer Ťyf paraffin wax, and a substantial covering of plaster of Paris above this.